Clean up temp files more thoroughly after testing. (#7815)

Our test cases spew a lot of files and directories around $TMPDIR.  Make more
thorough use of the testing package's TempDir methods to ensure these are
cleaned up.

In a few cases, this required plumbing test contexts through existing helper
code. In a couple places an explicit path was required, to work around cases
where we do global setup during a TestMain function. Those cases probably
deserve more thorough cleansing (preferably with fire), but for now I have just
worked around it to keep focused on the cleanup.

internal/inspect/inspect_test.go

@@ -28,7 +28,7 @@ import (
 )
 
 func TestInspectConstructor(t *testing.T) {
-	cfg, err := config.ResetTestRoot("test")
+	cfg, err := config.ResetTestRoot(t.TempDir(), "test")
 	require.NoError(t, err)
 	testLogger := log.TestingLogger()
 	t.Cleanup(leaktest.Check(t))
@@ -43,7 +43,7 @@ func TestInspectConstructor(t *testing.T) {
 }
 
 func TestInspectRun(t *testing.T) {
-	cfg, err := config.ResetTestRoot("test")
+	cfg, err := config.ResetTestRoot(t.TempDir(), "test")
 	require.NoError(t, err)
 
 	testLogger := log.TestingLogger()